Percussion has been used routinely during chest examination for many years. Using this technique, a trained clinician is able to distinguish underlying clinical abnormalities by observing the characteristic sounds radiated in response to a sharp tap to the body surface at the point being examined. Using this technique, a great deal of information can be obtained which relates to the condition of the lung, abdominal and other organs. Clinical abnormalities such as complete lung collapse (pneumo-thorax), regional lung collapse (atelectasis) and gas trapping in the bowel can be detected.
When percussion is performed over different areas of the body, the sound radiated is variously described as dull (over the liver) or stony dull (associated with a pleural effusion) or as resonant (over the lung) or hyper-resonant (over the bowel). The mechanism by which the variation in radiated sound occurs is not fully understood. However, it seems likely that the observed “resonance” following percussion of the lung, bowel or other tissue results from the presence of gas, and that the high compliance of the gas decreases the mechanical damping of the overlying tissue. This has the effect of increasing the mobility of the overlying tissue and allowing it to resonate following the percussive tap. Conversely, where the sub-tissue environment contains principally fluid, the tissue damping will be increased and the mobility decreased, resulting in a “duller” percussive sound.
In infants, the tissue in the chest is highly compliant and percussion is more difficult to perform. This is in part due to the fact that the force delivered in each tap must be limited to avoid causing injury to the infant. Further, the adult finger that is used both as a coupling device and sounding board between the infant's body surface and the percussing finger is too large to be used in tiny infants. Currently, no method exists which can be safely applied to the newborn infant and which provides useful information similar to that which is obtained using traditional percussive techniques which are applicable for adults.